Functional heterogeneity of the human blood-tumor barrier phenotype induced by patient-derived glioblastoma spheroids

The fundamental limitation to effective chemotherapy in Glioblastoma Multiforme (GBM) is the highly restrictive nature of the Blood-Tumor Barrier (BTB). The BTB functions as a robust regulatory interface, tightly controlling the efflux and influx of compounds and greatly restricting therapeutic access to the tumor microenvironment. We hypothesize that the BTB's functional phenotype is not static but is dynamically modulated by tumor characteristics. This observed heterogeneity is clinically actionable: tailoring drug delivery strategies to match individual tumor profiles is essential for improving prognosis. Thus, compiling a comprehensive database correlating BTB transport characteristics with molecular profiles is necessary to inform rational drug delivery design and optimize clinical outcomes. This study was designed to systematically outline the functional heterogeneity inherent in BTB transport mechanisms, comparing phenotypes induced by two separate Patient-Derived GBM Spheroid (PDS) in vitro transwell system. Our human model utilized iPSC-derived Brain Microvascular Endothelial-like Cells (hiPSC-BMECs) co-cultured with the two PDS samples to accurately model the complex neurovascular unit. We utilized a multi-modal functional assessment evaluating barrier integrity, paracellular transport, transcellular permeability, and efflux profile, to comprehensively characterize both the passive "leakiness" and active "tightness" of the BTB. These findings confirm that patient-specific GBM spheroids induce demonstrably heterogeneous BTB functional phenotypes. Junctional integrity is modulated by PDS co-culture, with heterogenous responses corresponding with GBM molecular profile. With limited paracellular “leakiness” and dysregulated active transport seen in both pinocytotic and efflux mechanisms. Current clinical assessment of BTB disruption relies primarily on Gadolinium enhancement on MRI, which only detects gross barrier breakdown. It fails to characterize the subtle, active, and heterogeneous transport mechanisms that significantly impede drug concentration in the tumor mass. Our in vitro approach provides a necessary, precise translational tool capable of characterizing the BTB's function from a patient's tumor sample, facilitating the development of truly personalized and effective drug delivery strategies in GBM therapy.